This invention relates to epoxy compounds, and in particular, to epoxy resins which contain polymeric materials contained therein.
Epoxy compounds, and in particular epoxy resins, comprise a well-known class of thermosettable resins. Such epoxy compounds possess excellent physical and chemical properties, and are particularly useful in a wide variety of applications. For example, epoxy resins are useful as coatings for a variety of substrates, laminates, moldings, adhesives, and in numerous other applications where a material exhibiting good heat resistance, hardness, electrical properties, dimensional stability, corrosion resistance and chemical resistance is desirable.
Unfortunately, typical epoxy thermoset compounds lack toughness and can exhibit brittleness. Attempts have been made to strengthen or reinforce epoxy resins by incorporating therein a variety of elastomeric materials. Examples of toughened epoxy resins are disclosed in U.S. Pat. Nos. 3,923,922; 4,221,697; 4,117,038; 3,856,883; 3,496,250; 4,082,895; 3,496,250; 3,316,195; 3,499,949 and 3,509,086; as well as European Patent Application No. 78,527, published Nov. 5, 1983: and Japanese Patent No. 55-018401.
A summary of epoxy and elastomeric blend technology is provided in Rubber-Modified Thermoset Resins, American Chemical Society (1984). Primarily, attempts to toughen epoxy compounds have focused on employing liquid rubbers, such as carboxyl-terminated butadiene-acrylonitrile copolymers. In certain amine cure systems, the rubber separates into distinct particles. However, the rubber must first be prereacted with the epoxy resin to ensure compatibility, and optimum cure properties, and such rubbers do not exhibit latent reactivity to the resins.
Epoxy resin and acrylonitrile butadiene styrene graft polymer blends are disclosed in U.S. Pat. No. 3,496,250. The rubbery backbone comprises from about 60 to about 10 weight percent and the the grafted polymers comprise from about 40 to about 90 weight percent of the graft polymer composition. The two components are typically placed in solution by adding them to a solvent. The blends are useful as adhesives in the form of a film solution. However, the resin-graft polymer blends do not have latent reactivity with the resin.
Unfortunately, toughened epoxy compounds typically exhibit poor heat resistance. In addition, toughened epoxy compounds can exhibit varying physical properties because commonly used elastomeric materials can vary in particle size distribution and/or behavior. Furthermore, the elastomeric materials which are incorporated into the epoxy compounds can act as plasticizers which in turn provide undesirable stability problems to the toughened compound.
In view of the deficiencies of the prior art, it would be highly desirable to provide a rubber-modified epoxy compound which is capable of good toughness without significantly sacrificing heat resistant properties.